On Mon, Feb 13, 2017 at 09:55:50PM +0800, Yubin Ruan wrote: > It have been mentioned in the book that there are three kinds of > memory barriers: smp_rmb, smp_wmb, smp_mb > > I am confused about their actual semantic: > > The book says that(B.5 paragraph 2, perfbook2017.01.02a): > > for smp_rmb(): > "The effect of this is that a read memory barrier orders > only loads on the CPU that executes it, so that all loads > preceding the read memory barrier will appear to have > completed before any load following the read memory > barrier" > > for smp_wmb(): > "so that all stores preceding the write memory barrier will > appear to have completed before any store following the > write memory barrier" > > I wonder, is there any primitive "X" which can guarantees: > "that all 'loads' preceding the X will appear to have completed > before any *store* following the X " > > and similarly: > "that all 'store' preceding the X will appear to have completed > before any *load* following the X " > > I know I can use the general smp_mb() for that, but that is a little > too general. > > Do I miss/mix anything ? Well, the memory-ordering material is a bit dated. There is some work underway to come up with a better model, and I presented on it a couple weeks ago: http://www.rdrop.com/users/paulmck/scalability/paper/LinuxMM.2017.01.19a.LCA.pdf This presentation calls out a tarball that includes some .html files that have much better explanations, and this wording will hopefully be reflected in an upcoming version of the book. Here is a direct URL for the tarball: http://www.rdrop.com/users/paulmck/scalability/paper/LCA-LinuxMemoryModel.2017.01.15a.tgz Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe perfbook" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
